Electrical converter



June' 12, 1928.

P. G. GIRAULT ELECTRICAL CONVERTER Filed Dec 14. 1922 InVentorz, peu.|G. Girault. by

W His Attorney.

Patented June 12, 1928 .UNITED STATES P'ATENT OFFICE.

PAUL GABRIEL GIBAULT, OF PARIS, FRANCE, ASSIGNOR T GENERAL ELEdTRIC COM-PAN Y, A CORPORATION OF NEW YORK.

ELECTRICAL CONVERTER.

Application flled'necember 14, 1922, Serial No. 606,950, and in FranceMay 31, 1922.

My invention relates, to alternating current dynamo electricmachines,andmore in particular to such machines as are used to transform balancedpolyphase currents to unbalanced polyphase currents or to a singlephasecurrent, and vice versa. v

It is often desirable, for example for the operation of electric weldingmachines, to take one or more relatively large single- ]0 phase loadsfrom a polyphase distributing system. When this is done it is desirableto provide apparatus whichwill take a balanced; load from the polyphasecircuit and deliver a single-phase current or an unbalanced polyphasecurrent to the load in question in order to preserve a balancedcondition on the polyphase system. One such apparatus is a setcomprising a polyphase motor connected'to the polyphase system and a gosingle-phase generator supplying a singlephase load. It has also beenproposed to provide separate 'windings on. a common stator, one windingbeing supplied from a polyphase source and the other winding sup- 5plyingthe single phase load, both windings cooperatin with a revolvingfield. My invention re ates to the latter class, and its primary objectis to arrange the two wind-' in s so that there is a minimum of mutual 0in uctance between the two stator windings, but a very close magneticcoupling between the stator windings and the rotating field, wherebyexchanges of power from one system to the other may be accomplishedefii- 5 ciently without unbalancing the polyphase system.

The features of my invention, which I believe to be novel andpatentable, will be pointed out in the claims appended hereto.

The preferred apparatus and manner of carrying my invention into effectwill now be explained in connection with the accompanyin drawings, in.which Fig. 'l represents t e electrical connect-ions of a threephase,single-phase asynchronous machine;

Fig. 2 the electrical connections of athreephase, three-phasesynchronous machine; Fig. 3 one manner of preventing mutual inductancebetween the two stator windings of either of the machines represented inFigs. 1 and 2; Fig. t-represents a portion of a stator showing a slotarrangementfor preventing mutual inductance between two sets ofdifferent phase windings therein; and M Fig. 5v is a vector diagram tobe referred to in connection with the arrangement of Fig. 4

Referring to the drawings, the armature of my machine comprises aprimary winding 1, preferably a stator winding, connected to the supplysystem 2, a secondary winding 3, carried by the same magnetic corestructure 4 as the first mentioned winding and connected to .the load 5.For the purpose of illustrating my invention, the winding 1 will betaken as a polyphase winding connected to a balanced polyphase system 2;in Fig. 1 the winding 3 as a single-phase winding supplying] asingle-phase load 5; and in Fig. 2, the secondary winding3 will be takenas a polyphase winding supplying an unbalanced polyphase load 5. Thelield of my machine, or the part which transfers energy from onearmature winding to the other, is preferably the rotor and consists ofan induction motor secondary 6 here shown as of the squirrel ca e type,but which may, for the purpose 0% starting, be of the wound rotor type.The machine'may. be asynchronous, as above described, or it maysynchronous, in which case it comprises, in addition to the threewindings mentioned above, a fourth winding 7',carried'on the fieldmember in conjunction with the squirrel cage winding for producing afield of definite polarity. lVhen the field member is the rotor thewinding 7 will be connected through slip rings 8 and brushes 9 to asuitable direct current source 10.

The invention will be explained by taking the case of convertingpolyphase into singlephase or vice versa with the sam frequency, but allthat issaid will be equall? applicable for secondary polyphaseunbalanced current and also for different frequencies on the primary andsecondary. In order to carry out the objects of my invention it isessential that the dissymmetries in thevalues of the polyphase currentspassing through the first winding when it is loaded and in operation bereduced to the lowest possible value. In order to attain this end itwill be necessary to eliminate the fluxes which are liable to disturbthis polyphase symmetry. These fluxes are, first, the parasitic rotatingflux due to the simple alternating current winding; and second, thefluxes common to the two stator windings, polyphase and singlephase,which do not pass through the rotor. In order to reduce the rotatingparasitic flux, it is, desirableto employ a tertiary winding,pr'et'er'ablya squirrelscage winding, 01" low resistance, andto have averylow coeflicient of leakage, that is to, say, coeflicients ofleakagewhich are lowfor the stator secondary winding and for the rotor tertiarywinding. This assumesv a low re; luctance in a radial direction and highleakage reluctance, a constructionsimilarjto th used in well designedinduction motors. In order. to reduce therfluxes which, are common tothe two stator windings but which do not passthrough therotor, thefollowing means andsecondary windings and for the Zones, of separation;third, ,to separate the coils of the two primary andrsecondary windingsin- 0, groupslasfar from eachother as possible; fourth, in thelattercase to, separate. the groups, of coils of the two windings; bypurely magneticscl'eensr i .ings arewound in separateigroups it mayQWhenthe primary and secondary wind happenthatrluring the startingperiod the motor-will stick atgareduced speed correspondingvto a;fieldharmonic; Thisxdifficulty may be remedied by usingthe. ,tWo statorwindings-at starting. Inthecase 0.1; a three phase singleaph'asemachine, it would be possible, for example, to makeup the .two

windings ofjidentical polyph-ase parts, connectthem-in doublestar, forstarting. and then for operating as a converter connect the polyphasesections. whichis to constitute the single; phase, winding, either inseries 7 with one phase reversed a or in delta with one of theconnections at the ,apexl-of the triangle and the other co nection atthecenter ofsthe opposite phase. This is ,possible windings i'epresentedinFig, 2. Two modificationvsafor preventing mutual with the inductionbetween the two, ,statore windings havebeen illustrated. InZFig. 3 thearmature windings 1 and 3 are entlrely separated,

exceptfor the coupling ]-p r o duced. by the common squirrel cage rotor6.; An; unbalanced polyphase load,.su ch as represented in Fig. 2, or asingle-phase load, as ineFigal, drawn from a corresponding winding 3 onthe, machine shown in, Fig. 3 wouldtl1ei'eboth halves of the l otor6might be provided" withv a direct current fieldlwinding for thecorrection of powerfactor or voltagereguffore have littleif anyefie'cton'the balance of acthe system frompwhich the polyphase windinglfissupplied. If desirable, one or atiq a a with a three-phase winding,and "slots "02 and igether, a resultant current representediby the Themodification shown in Fig, 4 represents one half of a fOUDPOlGstatonmagnet with the slots arranged for carrying out my invention.Slots a, .b andc willibeprovided 7U g] will contain either separatesingle-phase windings supplying separate single-phase loads or thesewindings may be connected in series in amannen to giire a resultantsinglephase current Thus in Fig. 5, let the line 7 d, 6 represent thecurrent produced byx a winding inislotsiwyand-e, thecurrent pro: ducedby theiwindingrin. slots Then it these windings. are properly.connected. toe

line d, f will flow. Separating. the'slotsim and f/ from: the threephasejgroups a, hand 0 are dead slots 11, designeditotpreventmutualinduction between the polyphase i and: singlephase groups. This,construction still per} 35 nitsavery close magnetic union betweenthearmatureawindings: and theasquirrels cage I rotor; and is efiectiye. inaccomplishing in; a

largeJ-measurethe. object: desired, #In each case the supply system alsofurnishes the energyfor producing rotation' and overcomingth'e losses.in the:con verter.; Q

The present; invention has particularly in QvieWHtheI applications;tQ-electrie Welding heating rivets, electroemetallurgsy:andzeleetro-chemistry, -but it is 7 not restricted thereto,- In,certain: of: these applications, v thexmagnetic power absorbed by; adevice may be: high. It .Wlill;.be: possibletirrtthis case. to workagainstithisiabsorptionotrmag- =1ou netic-v powernby all the. means:known; -particularly' in the case of small; installations, it: will bewell .to arrange in, parallel; with theprimary of the device, eitherdirectly or through thetransformer, a battery of condensers making .r itpossible.- to obtain-a 7 power factor of the devices as ;a. whole whichissatisfactory: both as amom'entarys value and a .mean value;- In thesecondary: circuit ltxWllldOQ usefulto employ variable contacts on thewinding and also an auto-transtorm'erwhich makes it possible; to;-;ob.tai-n a range of potentials WlllCllKlSdQSlIflb'lQ fol certainapplicationslnwthe case where there are several single -phase;consumption devices supplied by the secondary winding,

the secondary windings-may beiifurnished with as many pairs.ofldiametricallyopposite principal contacts. as rt-hjere i arecircuits: to

be supplied these, contacts; will; preferably be equidistant. so,astohave a pureapolyphase to the construction; ordinarily adopted, but 1the. respective functions of these members may of course be reversed. l

' .What Iclaim as newand gdesireltosecure byvLetters Patent of theUnitedgStates is :i

1. Adynamoelectricimaohine Comprising a plurality of mutuallynon-inductive, alternating current armature windings mounted on a commonmagnetic core, and a shortcircuited winding rotatively mounted in closemagnetic relation with respect to all of said armature windings.

2. A dynamo electric machine provided with a pair of mutuallynon-inductive, alternating current armature windings mounted on a commonstator, a short-circuited Winding rotatively mounted with respect to andin close magnetic relation with both of said armature windin s, andmeans for producing a field of definite polarity in combination withsaid short-circuited Winding.

3. A dynamo electric machine comprising a magnetic core and a pluralityof distributed alternating current armature Windings thereon, saidwindings being separated by magnetic barriers consisting of deep openslots in said core to prevent mutual inductance between said windings.

' In Witness whereof, I have hereunto set my hand this 27th day ofNovember, 1922.

PAUL GABRIEL GIRAULT.

